1. Field of the Invention
The present invention relates to a flow rate control valve. In particular, the present invention relates to a flow rate control valve which constitutes, for example, a mass flow controller and which makes it possible to control the flow rate of a fluid highly accurately and stably.
2. Description of the Related Art
It is required to highly accurately control the flow rate of a process gas to be supplied to a process equipment, for example, for a thin film-forming apparatus and a dry etching apparatus used in the process for producing semiconductors. Therefore, a mass flow controller for controlling the flow rate of the process gas is inserted into a tube passage for supplying the process gas to the process equipment. In such a case, the mass flow controller is provided with a flow rate control valve which is constructed such that the flow rate is regulated depending on a value of a control voltage.
The flow rate control valve concerning the conventional technique comprises, for example, a valve body which is formed with a flow passage for the fluid, a valve head which is displaceable with respect to the valve body, for regulating the flow rate of the fluid passing through the flow passage, and an actuator which is connected to the valve head, for displacing the valve head.
Recently, realization of practical use is advanced for a flow rate control valve provided with a piezoelectric actuator as the actuator.
In general, the displacement amount, which is brought about by the piezoelectric actuator, is minute. Therefore, in the case of the flow rate control valve provided with the piezoelectric actuator as described above, it is feared that the following inconveniences arise due to shortage of the stroke of the valve head.
(1) The controllable flow rate range is minimized.
(2) Any clogging occurs due to dust or the like.
(3) When the flow rate control valve is used for the mass flow controller, the time required for maintenance based on the use of the cleaning gas (for example, nitrogen gas) is increased.
A general object of the present invention is to provide a flow rate control valve which makes it possible to increase the stroke of a valve head as compared with a flow rate control valve concerning the conventional technique.
A principal object of the present invention is to provide a flow rate control valve which makes it possible to control the flow rate of a fluid highly accurately and stably.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.